Pattern transfer device using PC projector

ABSTRACT

A projection exposure apparatus comprising: a display device having a reflection-type or transmission-type display portion on which a predetermined image to be exposed is displayed; a stage for holding a substrate to be exposed; and a telecentric-type projection lens for projecting the predetermined image displayed on the display portion onto the surface of the substrate held on the stage.

TECHNICAL FIELD

The present invention relates to a projection exposure apparatus for usein a photolithography process, capable of transferring a desiredpattern.

BACKGROUND ART

Mask aligners and steppers (reductive projection exposure apparatus) areknown as lithographic projection exposure apparatuses. The former is anapparatus for exposing a reticle mask pattern for a wide area at a time,and is an essential apparatus for fabrication of liquid crystal device,ensuring an accuracy of 0.8 μm or higher on the line-and-space basis.The latter stepper is dedicated to a semiconductor process, whichreductively forms an image of a reticle mask pattern corresponding toeach device size, ensuring an accuracy of 0.18 to 0.5 μm or around onthe line-and-space basis.

Using the former mask aligner for research and development of devices,however, makes it difficult to rapidly repeat trial-and-errorexperiments since the reticle is very expensive and requires a very longtime of period for delivery thereof. There is also known a relativelyinexpensive manual-operation-type mask aligner, operation of whichhowever requires a great deal of skill since alignment and so forth mustbe achieved manually, so that reproducibility in the experimentalresults tend to vary depending on the level of skill in the operation.

Also the latter stepper is not practical for use in research anddevelopment since it suffers not only from the same problems in thereticle fabrication, but also from problems that the apparatus isexpensive, that a facility environment around the apparatus needs a verysevere control, and that its full-automatic nature makes it difficult tobe applied to purposes other than semiconductor process.

It is therefore an object of the present invention to provide aprojection exposure apparatus for research and development, which iscapable of readily transfer a desired pattern, and moreover featured byits compactness, inexpensiveness and easy operation.

DISCLOSURE OF THE INVENTION

To solve the aforementioned problems, a projection exposure apparatus ofthe present invention comprises a display device having areflection-type or transmission-type display portion on which apredetermined image to be exposed is displayed; a stage for holding asubstrate to be exposed; and a telecentric-type projection lens forprojecting the predetermined image displayed on the display portion ontothe surface of the substrate held on the stage.

In the projection exposure apparatus, the projection lens projects apredetermined image displayed on the display portion onto the surface ofthe substrate held on the stage, so that a desired image can readily betransferred onto the substrate. That is, the display device cantypically be composed of a liquid crystal display device, which iscapable of readily altering display of the predetermined image inresponse to electric input signals, and such display device iscommercially available at a low cost, which makes it more easier toalter design or specification in the phase of research and development,as compared with the case where a reticle which is very expensive andrequires a very long time of period for delivery is used. In addition,use of the projection lens of telecentric type can reduce influence onimaging magnification of transferred image on the substrate even underthe presence of a slight alignment error in the direction of the opticalaxis, and enables pattern transfer with an excellent reproducibility.

In a preferred embodiment of the foregoing apparatus, the projectionlens has a zoom optical system for varying magnification of theprojection lens, and the zoom optical system has a variablemagnification mechanism based on an inner driving system.

Because the projection lens has the zoom optical system for varyingmagnification of the projection lens, and the zoom optical system hasthe variable magnification mechanism based on the inner driving system,the apparatus makes it possible not only to transfer a predeterminedimage displayed on the display portion properly with a desiredmagnification onto the substrate held on the stage, but also to improvethe workability since the working distance does not vary during thevariable magnification operation.

In a preferred embodiment of the foregoing apparatus, the apparatusfurther comprises a stop control mechanism for controlling a size of anaperture stop provided in the projection lens.

Because the apparatus herein further comprises the stop controlmechanism for controlling size of the aperture stop, the resolution canbe altered depending on control of the stop control mechanism, torelatively smoothen the contour of a projected image projected onto thesubstrate even if the predetermined image displayed on the displayportion has a jagged contour expressed by connected dots of matrix.

In a preferred embodiment of the foregoing apparatus, the apparatusfurther comprises a control computer for supplying an image datacorresponding to the predetermined image to the display device, andswitching a dot-matrix-type display status of pixels provided on thedisplay portion into a display status corresponding to the image data.

By using the control computer, the image data supplied to the displaydevice can be corrected or altered in an easy-and-rapid manner, andtherefore it is possible to improve operability of the projectionexposure apparatus.

In a preferred embodiment of the foregoing apparatus, the display devicecan preferably be composed of a liquid crystal display device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view for explaining a general constitution of the projectionexposure apparatus of the embodiment;

FIG. 2 is a view for explaining an optical system of the apparatus shownin FIG. 1;

FIG. 3( a) shows a transfer pattern, and FIG. 3( b) shows a projectedimage with a resolution controlled; and

FIG. 4 is a view for explaining a principal portion of the projectionexposure apparatus according to the second embodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic view for explaining a constitution of theprojection exposure apparatus according to a first embodiment of thepresent invention.

The projection exposure apparatus comprises a stage 10 for holding asubstrate W which is the object to be exposed; a liquid crystal displaydevice 20 in which a transfer pattern to be exposed onto the substrate Wis displayed on a liquid crystal panel 21 which is a liquid crystaldisplay portion; a telecentric-type projection lens device 30 forprojecting the transfer pattern displayed on the liquid crystal panel21, onto the surface of the substrate W held on the stage 10; and acomputer 40 for regulating and controlling the entire operations of theprojection exposure apparatus.

The stage 10 can move the substrate W within the X-Y plane, and also inthe direction of the Z-axis. The stage 10 is further designed to berotatable around the X-axis and Y-axis so as to control a tilt angle ofthe substrate W. Positions of the substrate W held on the stage 10 inthe X-Y plane or in the Z-axis direction, and the tilt angle of thesubstrate W are controlled by the computer 40 based on measured resultsoutput from an alignment unit 50.

The alignment unit 50 can optically detect the position and the tilt ofthe stage 10 by reading marks formed on the stage 10, or by irradiatingan inspection light to the substrate 10, or the like. Use of suchalignment unit 50 enables an automatic alignment of the substrate W withrespect to the projection lens device 30, to provide a full-automaticprojection exposure apparatus.

The liquid crystal display device 20 herein is a commercial liquidcrystal projector, and comprises the liquid crystal panel 21 of atransmission-illumination-type which includes pixels having a dot matrixpattern to display a desired transfer pattern; a drive circuit 22 fordriving the liquid crystal panel 21 to thereby switch ON/OFF display ofthe individual pixels; and an exposure light source device 23 forilluminating the liquid crystal panel 21 from the back side. The liquidcrystal panel 21 herein serves as a mask for displaying the transferpattern.

The projection lens device 30 comprises a first imaging system 31 foronce imaging the transfer pattern displayed on the liquid crystal panel21 of the liquid crystal display device 20 to thereby form anintermediate image; a second imaging system 32 for projecting theintermediate image formed by the first imaging system onto the substrateW at a desired magnification; and an observatory optical system 23 forobserving an image formed on the substrate W. The second imaging system32 is a telecentric-type zoom optical system capable of varyingmagnification of the projection lens device 30 typically in three steps,and has a constitution in which a variable magnification mechanism basedon inner drive system and an aperture stop control mechanism areincorporated into to an objective lens 32 a. A lens control unit 52herein controls the magnification of projection of the projection lensdevice 30 by driving the variable magnification mechanism provided tothe objective lens 32 a according to instructions from the computer 40.At a position between the first imaging system 31 and second imagingsystem 32, and whereat the intermediate image of the liquid crystalpanel 21 is formed by the first imaging system 31, provided is anelectromagnetic shutter 37. The shutter 37 is driven by a shutter drivemechanism 38 and is opened only during light exposure. To anobservational optical system 34, an illumination light source device 36is connected through a fiber 35.

The computer 40 used for control is a personal computer which is shiftedfrom the one attached to a commercial liquid crystal projector, and iscapable of controlling operation of the liquid crystal display device 20so as to display a desired transfer pattern on the liquid crystal panel21 which serves as a mask. Using a CAD or an image processing softwarepre-installed on the personal computer allows an easy and rapidalteration of the transfer pattern on the liquid crystal panel 21 andalso allows statistical management of a huge volume of data related tothe transfer patterns before and after the alteration. The computer 40is also arranged to control operation of the lens control unit 52according to display status of the transfer pattern on the liquidcrystal panel 21 so as to control the reduced magnification or numericalaperture of the objective lens 32 a.

FIG. 2 is a view for explaining specific optical elements composing theprojection lens device 30, liquid crystal display device 20 and soforth. The exposure light source 23 comprises a lamp 23 a for emittingultraviolet light necessary for the exposure, and a parabolic mirror 23b for converting the exposure light from the lamp 23 a into a parallelbeam to become incident to the liquid crystal panel 21. The exposurelight goes out of the front surface of the liquid crystal panel 21 onlythrough transparent pixels according to the transfer pattern, while theliquid crystal panel is illuminated by the exposure light from the backsurface thereof. The exposure light went out through the transparentpixels on the liquid crystal panel 21 is converted into a parallel fluxthrough the lens L1 and deflected by a reflective mirror M1 into thevertical direction, and condensed through a lens L2. At the positionwhere an intermediate image is formed by the lens L2, theelectromagnetic shutter 37 is disposed. The exposure light which passedthrough the shutter 37 is converted into a parallel beam through a lensL3 which is a field lens, and is then reflected by a dichroic mirror M2incorporated in a beam splitter so as to be deflected in the verticaldirection, and is condensed onto the wafer W through the objective lens32 a. As a result, a reduced image of the transfer pattern formed on theliquid crystal panel 21 and the like are projected on the wafer W. Thismakes it possible to expose a resist layer on the wafer W according tothe transfer pattern.

On the other hand, the illumination light supplied through the fiber 35is reflected by a half mirror M3, passes through the dichroic mirror M2and illuminates the wafer W through the objective lens 32. The lightscattered at the individual points on the wafer W is converted into aparallel beam by the objective lens 32 a and passes through the dichroicmirror M2 and the half mirror M3, and is then condensed by an imaginglens L5 to be incident into a CCD camera 34 a. This enables observationof the wafer W by using a wavelength different from that of the exposurelight.

The first imaging system 31 comprising the lenses L1 and L2 is anoptical system of dual-telecentric type, and the second imaging system32 comprising the lens L3 and objective lens 32 a is also ofdual-telecentric type. In addition, the wafer-side lens of the objectivelens 32 a is fixed to thereby keep the working distance always constant.An aperture stop VA provided in the objective lens 32 a is automaticallycontrolled according to the magnification of projection, so as to keepan optical brightness (effective F-number) constant.

In one specific exemplary design, the focal length of the lens L1 wasabout 150 mm, the focal length of the lens L2 was about 70 mm, and thefocal length of the lens L3 was about 200 mm. In addition, the focallength of the objective lens 32 a was designed to be variable amongthree steps, that were 2 mm, 20 mm and 100 mm. When the focal length ofobjective lens 32 a is set at 2 mm and the NA thereof is 0.5, a 1/100reduced image can be formed. When the focal length of the objective lens32 a is set at 20 mm and the NA thereof is 0.26, a 1/10 reduced imagecan be formed. When the focal length of the objective lens 32 a is setat 100 mm and the NA thereof is 0.055, a ½ reduced image can be formed.

The aperture stop VA provided in the objective lens 32 a can also beused for adjusting the resolution. FIG. 3 is a drawing for explainingrelationship between a transfer pattern displayed on the liquid crystalpanel 21 and a projected image formed on the substrate W. FIG. 3( a)shows one pattern displayed on the liquid crystal panel 21, and FIG. 3(b) shows a resultant projected pattern. While, as shown in FIG. 3( a),the transfer pattern has a smooth contour for the portion extendingalong the longitudinal and transverse directions, it has a jaggedcontour at the obliquely extending portion. The diameter of the aperturestop VA provided in the objective lens 32 s is then controlled tothereby intentionally degrade the resolution. FIG. 3( a) is a view forexplaining the projected image formed on the substrate W as a result ofintentionally degraded resolution. This successfully results in arelatively smooth contour even for such obliquely extending portion onthe liquid crystal panel 21. Since the transfer pattern is projectedonto the substrate W using the telecentric-type projection lens device30 in the present embodiment, it is advantageous in that themagnification or the like does not vary even when the aperture stop VAis controlled so as to alter the resolution.

Operation of the projection exposure apparatus shown in FIGS. 1 and 2will be described below. First, the substrate W is set on the stage 10while keeping the shutter 37 closed. Next, an appropriate command isentered to the computer 40 to thereby align the substrate W on the stage10 with regard to the projection lens device 30. Next, a desiredtransfer pattern is displayed on the liquid crystal panel 21 by usingpattern data related to any image stored in the computer, newly-enteredpattern data, or the like. Next, the lens control unit 52 is operatedusing magnification data or stop data, which are preliminarily stored inthe computer 40 to thereby set the projection magnification to anecessary value and set the resolution to an appropriate value. Next,the shutter 37 is opened at a proper timing only during an exposureperiod based on data related to the exposure period stored in thecomputer 40. By such operation, the transfer pattern on the liquidcrystal panel 21 illuminated by the exposure light source device 23 isprojected onto the substrate W through the projection lens device 30.The resultant projected image on the substrate W is what is obtained byenlarging or reducing the transfer pattern at a desired magnification,and what is obtained by smoothening the jagged contour by properlydegrading the resolution. By exchanging the substrate W for anothersubstrate W, the another substrate W can be exposed by steps similar tothe above-described ones. The projected image projected on the substrateW can be altered for each substrate W by only a simple operation ofentering an appropriate command to the computer 40.

Second Embodiment

Since the projection exposure apparatus according to the secondembodiment is a modified example of the apparatus according to the firstembodiment, only portions differed from those in the first embodimentwill be explained while omitting the repetitive explanation.

FIG. 4 is a view for conceptually explaining a constitution of a displaydevice 120 incorporated into the projection exposure apparatus accordingto the second embodiment. In this case, a display panel 121 having areflection-type DMD (digital micromirror device) is used, in place ofthe transmission-illumination-type liquid crystal panel 21 previouslyshown in FIG. 1, to display a desired transfer pattern thereon.

More specifically, the display panel 121 is illuminated from the frontface side by an exposure light coming from a lamp 23 a and a parabolicmirror 23 b. The display panel 121 comprises a large number of mirrorswhich are arrayed in a matrix form and are properly adjustable in theangles thereof. The display panel 121 is designed so that each of themirrors can be switched between a state of reflecting an incidentexposure light to the direction of the lens L1 and a state of reflectingthe incident exposure light to the direction deflected from the lens L1,with the aid of an unshown drive circuit. That is, when observed fromthe side of the lens L1, the display panel 121 has a desired transferpattern displayed thereon. As a result, a reduced image or the like ofthe transfer pattern formed on the display panel 121 is projected ontothe substrate W shown in FIG. 1, similarly to the case in the firstembodiment, so that a resist layer on the substrate W can be exposedaccording to the transfer pattern.

While the present invention has been explained referring to the specificembodiments, the present invention is by no means limited to theaforementioned embodiments. For example, an alignment unit 50 is not anessential one, and the alignment will be possible also through a manualoperation using the observational optical system 34 or the like.

It is also allowable to compose the second imaging system 32 withseparate zoom lenses individually each having a divisional zoom ratiosince a large zoom ratio of the second imaging system 32 tends toincrease various aberrations.

For the case where a necessary resolution cannot be obtained typicallydue to a large reductive magnification, it is still also allowable toset the projection lens device 30 to a fixed magnification and to varythe magnification based on the transfer pattern to be displayed on theliquid crystal panel 21.

INDUSTRIAL APPLICABILITY

As the above-described explanation clearly, according to the projectionexposure apparatus of the present invention, a predetermined imagedisplayed on the display portion is projected by the projection lensonto the surface of the substrate held on the stage, so that a desiredimage can readily be transferred onto the substrate. In addition, use ofthe telecentric-type projection lens allows pattern transfer with anexcellent accuracy and reproducibility.

The projection exposure apparatus of the present invention is thereforecapable of readily transferring a desired pattern, featured by itscompactness, inexpensiveness and easy operation, and is in particularsuitable as a projection exposure apparatus for use in research anddevelopment.

1. A projection exposure apparatus comprising: a display device having areflection-type or transmission-type display portion on which apredetermined image to be exposed is displayed; a stage for holding asubstrate to be exposed; a telecentric-type projection lens forprojecting the predetermined image displayed on said display portiononto the surface of the substrate held on the stage, and a stop controlmechanism for controlling the size of an aperture stop provided in theprojection lens, wherein the stop control mechanism controls theaperture stop so that a resolution of a projected image formed byprojecting the predetermined image onto the substrate is degraded tosmooth a contour of the projected image.
 2. The projection exposureapparatus as claimed in claim 1, wherein the projection lens has a zoomoptical system for varying magnification of the projection lens, thezoom optical system having a variable magnification mechanism based onan inner driving system.
 3. The projection exposure apparatus as claimedin claim 2, further comprising a control computer for supplying an imagedata corresponding to the predetermined image to the display device, andswitching a dot-matrix-type display status of pixels provided on thedisplay portion into a display status corresponding to the image data.4. The projection exposure apparatus as claimed in claim 3, wherein thecomputer controls the variable magnification mechanism.
 5. Theprojection exposure apparatus as claimed in claim 1, further comprisinga control computer for supplying an image data corresponding to thepredetermined image to the display device, and switching adot-matrix-type display status of pixels provided on the display portioninto a display status corresponding to the image data.
 6. The projectionexposure apparatus as claimed in claim 5, wherein the computer controlsthe stop control mechanism.
 7. The projection exposure apparatus asclaimed in claim 1, wherein the projection lens comprises an objectivelens and the objective lens comprises the aperture stop.
 8. Theprojection exposure apparatus as claimed in claim 1, further comprisingan observational optical system for observing the image projected on thesubstrate.